The invention relates to injection needle units for use on a syringe during patient administered injections. Such needle units comprise a hub fitting on a syringe and a needle mounted in the hub with pointed ends projecting from each end of the hub, i.e., a first end designed for penetrating the seal of a cartridge in a syringe and a second end designed for insertion into the skin of a patient to inject medicine from said cartridge.
Insofar as may people have needle phobia, which makes them reluctant to inject themselves, attempts have been made to develop needles which do not cause pain which can amplify this needle phobia.
Less pain by needle insertion is obtained by making the needles thinner and shorter. Whereas a lower limit for the length of the needles is set by the fact that an injection needle must be long enough to penetrate the skin and to deliver the medication subcutaneously, the limit for the thickness of the needle is set by the fact that a medicine shall be able to flow through the needle within an acceptable time and that the needle shall possess a mechanical strength so that it does not break or collapse when it is influenced by bending forces during the insertion and injection.
As it appears to be possible to make an insulin suspension and consequently other medicament solutions flow through needles as thin as G30 and even thinner, i.e. needles having outer diameters less than 0.320 mm and an inner diameter preferably larger than 0.13 mm, the mechanical strength sets the crucial limit for the thickness of a useable injection needle. Consequently, standards have been adopted which specify how much stainless steel injection needles for medical use are allowed to bend when influenced by defined forces.
It is an object of the invention to provided a needle having an outer diameter thinner than 0.320 mm which will not be in danger of breaking even when the limit sey by ISO 9626 are exceeded.
This is obtained by an injection needle unit for use on a syringe by patient administrated injections comprising a hub fitting on a syringe which hub carries a needle having a cross section diameter less than 0,320 mm and being mounted in the hub with pointed ends projecting from each end of the hub a first end designed for penetrating the seal of a cartridge in a syringe and a second end designed for insertion into the skin of a patient to inject medicine from said cartridge, wherein the needle according to the invention is made from an super elastic material which can obtain recovered elongation of more than 2% without having permanent deformation in the material. This elastic deformation can also be defined through Hooke""s law "sgr"=E xxcex5, where "sgr" is the strain, E is the Elasticity Modulus (Young""s Modulus or Secant Modulus) and xcex5 is the elongation. "sgr" and xcex5 will be proportional with constant E-modulus when having a fully elastic deformation phase.
Such a super elastic behavior will e.g., be beneficial during repetitive bending of the needle to angles exceeding the limits defined in ISO 9626. Needles made from such super elastic material can be bent at rather sharp angles without breaking or collapsing and will, after having been bent, return to their linear shape.
According to the invention the needle may be made from a super elastic material from a special group of materials which in a given temperature interval change their crystal structure.
According to the invention the super elastic material used may be a NiTi alloy.
The use of super elastic needles for syringes is known from Japanese patent application No. 5-96004, which concerns injectors for analytical purposes designated as micro syringes. Such syringes are used to accurately measure small volumes of samples for injection into measuring instruments, some of which are capable of measuring a volume on the order of 0.1 microliters.
The high form stability and stiffness of an NiTi alloy containing 50.2 to 52.0 at. % Ni is taken advantage of in a needle with a diameter of 0.5 mm which maintains its linear shape when the needle is inserted into a needle guide of the injection device on sample injection into the measuring instrument. It is important that the needle maintains its linear shape as the piston can be moved into the lumen of the needle.
In needles for subcutaneous injections it is important that the needle is thin. Needles thinner than 0.320 mm are aimed at whereas it is less important if the needle is bent during the insertion if only it can be ensured that the needle do not break or collapse. This makes it attractive to use an alloy with a higher Ni content as needles made from such an alloy are less stiff but very elastic so that large deformations can be tolerated without any risk for breakage.
According to the invention an alloy containing at least 52% Ni and consisting of the balance Ti and unavoidable impurities is found appropriate.
The properties, inbreakability and elasticity, of the needle may be further enhanced by adding at least one further element at a content not higher than 4%.
In excess of being practically unbreakable the NiTi needle in spite of its large Ni content has shown to have a better biocompatibility than has ordinary stainless steel for medical purposes. Further the torsion strength and the ultimate strength of a NiTi needle is appreciably higher than for a corresponding needle made from conventional stainless steel.
Alternatively the needle may according to the invention be made from a curable or thermoplastic polymer super elastic material.
The needle hub may be of the kind comprising a sleeve with an internal thread, which sleeve forms the attachment means and can be screwed onto an outer thread on an attachment part of a syringe, and which hub has a base carrying the sleeve and the needle. The needle is fixed in the base with an injection part projecting from one side of said base and a back needle projecting from the other side of the base, the back needle being surrounded by the sleeve which projects from the base perpendicularly to said base on the same side as the back needle. When the hub is screwed onto a pen, the back needle may penetrate a rubber membrane which closes an ampoule in the pen. A medicine, e.g., insulin, can now be administered from the ampoule through the needle.
In an embodiment of the needle hub a needle guide may be provided which needle guide has an abutment surface by which it can abut the skin where the injection is going to be made, and a needle guide channel opening through said abutment surface. The needle which is movable relative to the abutment surface can be moved through the needle guide to make a sharpened end of the needle project from said surface. When the surface abuts the skin the needle will project through the skin into the underlying tissue. The needle guide may hide the needle to the user and the abutment of the abutment surface may distract the user so that he hardly feels the sting when the needle is inserted.
A small cavity may be provided in the abutment surface around the opening of the needle guide which may fit to the outer diameter of the needle so that air but hardly liquid can pass between the needle and the guide. The opening may be covered by a transparent cover plate which is frosted on its side facing the cavity. Before insertion of the needle its sharp end is positioned in the cavity beneath the cover plate. When a hub with a needle guide and with the above mentioned cavity covered with a frosted cover plate is mounted on a syringe it may be used as an air shot indicator. Air shots are made to ensure that air is driven out of the ampoule and the needle before attempt are made to inject medicine. To make an air shot a small dose is set and is pressed out through the needle the syringe being held with the injection part of the needle pointing vertically upward. This process is repeated until a thin jet of liquid is seen to leave the sharp end of the needle. When a needle with an air shot indicator of the above mentioned kind is used, air from the needle will pass away through the narrow gap between needle and needle guide. When liquid leaves the sharp end of the needle the cavity will quickly be filled and wet and the frosted surface which will then change appearance to be more clear. When the needle is going to be inserted through the skin it is passed through the cover plate and into the skin.
In another embodiment, the cavity in which the sharp end of the needle is positioned and which is covered by a cover plate may contain a lubricant that allows the needle to penetrate the skin more easily, or the cavity may contain an anesthetic to make the needle insertion totally painless.
In still another embodiment, the elasticity of the needle may be taken advantage of by providing an enforced curved course of the injection part of the needle between the base of the needle hub and the needle guide. With the enforced curved course, the sharp point of the injection part is positioned immediately beneath the abutment surface which is held against the skin. When the needle is going to be inserted, the enforcement is released and the needle will due to its elasticity straighten itself and thereby move the sharp end through the skin. If the needle itself does not possess the force needed for the straightening and insertion of the needle, the straightening may be assisted by a conventional spring element.
To ensure that the super elastic back needle do not deflect when the needle hub is mounted on a syringe where the super elastic needle shall penetrate the rubber membrane sealing a cartridge in the syringe a reinforcement of the back needle may be provided.
The reinforcement of the back needle may comprise a plastic needle integral with the needle hub surrounding the back needle of the super elastic needle injection needle or it may be a conventional stainless steel needle mounted in the needle hub in continuation of the super elastic needle or surrounding the back needle of said needle.
An embodiment of a needle unit may, according to the invention, comprise a needle hub comprising a base having a first and a second side. A sleeve projects from the first side of the base and forms attachment means by which the needle unit can be mounted onto an attachment part of a syringe. A housing projects from the second side of the base, in which housing a plug is axially displaceable. A needle is fixed in the base with a part forming a back needle projecting from the first side of the base and being surrounded by the sleeve. The rest of the needle projects from the second side of the base and is surrounded by the housing. Further, the needle is fixed in the plug with an injection part projecting from a distal end of the plug and an intermediary part running between a proximal end of the plug and the second side of the base.
When the plug is moved into the housing, the needle is forced to bend out from its linear shape. If the plug is released the needle will seek to return to its linear form whereby the plug and the injection needle part is moved in a distal direction. When the needle unit is held with its distal end against the skin where an injection is wanted, said movement in the distal direction will make the injection needle penetrate the skin and be ready for an injection of a medicine through the needle.
To avoid sharp bending of the intermediary needle at the transitions between this needle and the base and between this needle and the plug, respectively, flared recesses may be provided around the needle in said base and said plug at said transitions. These flared recesses will guide the needle to attain a curved shape without sharp bending when it is bent away from its linear shape. A similar guiding, flared recess may appropriately be provided at the transition between the plug and the injection needle.